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Updated: June 23, 2025
The slug, called Succinea, is not strictly aquatic, but lives in damp places, and may be seen in full activity far from rivers, in meadows where the grass is wet with rain or dew; but shells of the genera Limnaea, Planorbis, Paludina, Cyclas, and others, requiring to be constantly in the water, are extremely exceptional in the loess, occurring only at the bottom of the deposit where it begins to alternate with ancient river-gravel on which it usually reposes.
Limnaea, similar to those of Europe, creep along the surface of the water; small Planorbis live on the water-plants, to which also adhere Ancylus; and Paludina, Cyclas, and Unio, furrow its muddy bottom. The latitude of this spot was 21 degrees 23 minutes S.
We have mentioned in the last chapter that the base of the Lower Lias is characterised, both in England and Germany, by beds containing distinct species of Ammonites, the lowest subdivision having been called the zone of Ammonites planorbis.
I should have studied the eggs of the Planorbis, a glairy nebula wherein focuses of life are condensed even as suns are condensed in the nebulae of the heavens. I should have admired the nascent creature that turns, slowly turns in the orb of its egg and describes a volute, the draft, perhaps, of the future shell. No planet circles round its center of attraction with greater geometrical accuracy.
These strata are of great thickness, perhaps a thousand feet in some places; and along with such shells as Paludina, Planorbis, and Limnæa are also found remains of various other animals, such as fish, serpents, batrachians, crocodiles, ruminants, and those of huge pachyderms, as Rhinoceros, Dinotherium, and Cænotherium.
These are, surely, in their imperfect and perfect states, food enough to fatten many a good trout: but they are not all. See these transparent brown snails, Limneae and Succinae, climbing about the posts; and these other pretty ones, coil laid within coil as flat as a shilling, Planorbis.
The croziers of some of the young ferns are very perfect, and were at first mistaken by collectors for shells of the genus Planorbis. On the whole, the vegetation of Bovey implies the existence of a sub-tropical climate in Devonshire, in the Lower Miocene period.
Along the shore were strewn shells thrown up by the surf; and on examining them, I found them all to belong to well-known old-world genera Unio, Planorbis, Ancylus, and Ampullari.
To some it may appear enigmatical how such fragile objects could have escaped annihilation in a river-bed, when flint tools and much gravel were shoved along the bottom; but I have seen the dredging instrument employed in the Thames, above and below London Bridge, to deepen the river, and worked by steam power, scoop up gravel and sand from the bottom, and then pour the contents pell-mell into the boat, and still many specimens of Limnaea, Planorbis, Paludina, Cyclas, and other shells might be taken out uninjured from the gravel.
One- eighth diameter of original. a. Side view. b. Front view, showing mouth and bisulcated keel. Ammonites planorbis, Sowerby. One-half diameter of original. Nautilus truncatus, Sowerby. Ammonites bifrons, Brug. Ammonites Walcotti, Sowerby. Ammonites margaritatus, Montf. Syn. Ammonites Stokesi, Sowerby.
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